1. Field of the Invention
The invention relates to thermal energy exchangers and, more particularly, to thermal energy exchangers adapted primarily for use in residential, commercial and industrial interiors for exchange of energy between stale air and fresh air.
2. Background Art
The concept of employing thermal energy exchangers for various applications is relatively well known. For example, thermal energy exchangers are used in industrial facilities for insuring that interior air does not build up to a dangerous level of pollutants or toxicity. It is also becoming known to utilize thermal energy exchangers in residential and general commercial applications. For example, thermal energy exchangers serve very useful purposes in restaurant facilities, particularly around kitchen areas where various types of cooking functions are being undertaken.
It is also known to employ thermal energy exchangers in applications such as vehicles. For example, it is known to employ vehicle thermal energy exchangers having a series of plastic tubes. The tubes are arranged in a series of mutually parallel rows, with a pair of plastic collector plates connected to the ends of the tubes. However, manufacture of the collector plates in single pieces can exhibit certain problems. For example, the high precision collector plates may need to be stamped with a relatively large number of holes (i.e. 200 to 2000). These holes may be of relatively small diameter, namely on the order of 1.5 to 5 mm. It is difficult to undertake such stamping processes, particularly when it is also necessary to undertake periodic checks for shrinkage and deformation. Still further, the stamping process must be undertaken while avoiding the presence of molding/dripping into the holes. Also, manufacture of each collector plate in a single piece makes it difficult to automatically insert the ends of the tubes in the holes of the collector plates.
To overcome these drawbacks, it is also known to undertake activities where each collector plate is constructed from a number of plastic terminal elements. The plastic terminal elements are overlapped and welded together. Each of the terminal elements includes a series of semi-circular seats separated from each other by bonding portions, suitable for being welded to corresponding bonding portions of a complimentary terminal element. The assembly procedure for this type of thermal energy exchanger starts from a first pair of terminal elements, engaging the ends of a first row of tubes in the semi-circular seats of the terminal elements. A second pair of terminal elements are then positioned above the first row of tubes, and the bonded portions of the terminal elements are then welded together. This operational sequence may be repeated a number of times, in correspondence to the number of rows of tubes that form the finished thermal energy exchanger.
With this process, adjacent terminal elements may be bonded together by means of welding, ultrasonic or comparable processes. These processes can cause the bonding portions in reciprocal contact to melt together. Also, such welding operations are extremely delicate, and require accurate calibration of the welding parameters. For example, if too much material is fused, flash which is formed by the plastic material can enter the ends of the tubes, thereby causing perforations. In turn, these perforations can result in heat exchange fluid leakage in the finished thermal energy exchanger. In contrast, however, if the space between the abutting surfaces of the bonding portions of the terminal elements is not completely closed during welding, a hermetic seal between the ends of the tubes and the collector plate is not achieved. Accordingly, in this case as well as the prior, the finished thermal energy exchanger may have heat exchange fluid leaks.
An attempt to overcome certain of the foregoing problems is disclosed in Mannoni, et al, U.S. Patent Application Publication No. U.S. 2002/0157817 A1, published Oct. 31, 2002. For purposes of description, reference will be made to the reference numerals utilized in the disclosure of the Mannoni, et al, patent application publication. Therein, Mannoni, et al, disclose a plastic thermal energy exchanger 10. The thermal energy exchanger 10 includes a number of tubes 12 forming a heat exchange core. The tubes 12 can be characterized as being formed of thin plastic “straws” arranged in a series of mutually parallel rows. The ends of the tubes are bonded and sealed to a pair of collector plates 14. Two tanks 16 and 18 are then bonded to the respective collector plates 14. The tank 18 is equipped with openings 20, providing for the inlet and outlet of heat exchange fluid.
Each collector plate 14 can be characterized as being formed by a series of plastic terminal elements 22. Each terminal element includes a first and second row of semi-circular seats 24 and 26. The seats 24 and 26 are separated from each other by bonding portions 28 and 30. Each terminal element 22 is equipped with a pair of space elements 32. In final assembly, the pair of space elements 32 will rest against a surface 34 of an identical terminal element 22. Assembly can be undertaken utilizing single layers. Each layer can be realized by means of an operational sequence. The operational sequence includes the following functional steps:                a. Preparing a first terminal element 22a.        b. Placing the ends of a row of tubes 12 in the seats 26 of the first terminal element 22a.        c. Offering up a second terminal element 22b, such that the ends of the tubes 12 engage with the seats 24 of the second terminal element 22b.        d. Welding the bonding portions 28 and 30 of the first and second terminal elements 22a and 22b, respectively, together along the welding plane or surface 34.        
For the Mannoni, et al, assembly, the welding plane or surface 34 represents or can be characterized as an “ideal” joint plane, allowing the semi-circular seats 24 and 38 which face each other to be united together. This assembly results in a formation of circular seats, with a diameter equal to that of the external diameter of the ends of the tubes 12.
Mannoni, et al, then go on to illustrate views of the two complimentary bonding portions 28, 30 which are to be bonded together by means of the welding process. Each bonding portion 28 of the terminal element 22a can be characterized as a butt surface 36, set back with respect to the welding plane 34. The volume between the welding plane 34 and the butt surfaces 36 of the terminal element 22a can be characterized as Va. Each bonding portion 30 of the terminal element 22b has a welding portion 38. The welding portion 38 projects beyond the welding plane 34. The volume of material of each bonding portion 30 projecting beyond the welding plane 34 is characterized as Vb. Mannoni, et al, then further disclose the concept that a “fill ratio” R can be defined as the ratio between the volumes Va and Vb. Mannoni, et al, then further describe the concept that the fill ration R would be in the range, for their embodiment, of 0.8 to 1.3.
Mannoni, et al, further describe and illustrate a bonding zone between the bonding portions 28, 30, after completion of welding. Mannoni, et al, further explain that the fact of having a fill ratio which is relatively close to unity allows the volume Va to be filled with material originating from the melting of volume Vb. Mannoni, et al, characterize this fact as permitting a substantially ideal bond between the terminal elements 22a and 22b. Mannoni, et al, also describe the concept that, in particular, problems of excess molten material occluding the ends of the tubes that are not completely sealed due to an insufficient amount of molten material, are avoided. To better describe this concept, Mannoni, et al, illustrate and describe a situation following a welding operation with a fill ratio that is considered to be too high. That is, the fill ratio is in excess of 1.3. In such a case, the excess molten material will exude laterally from the reciprocal mating surfaces of the bonding portions, and thus invade the spaces of the tubes. Such molten material may damage the walls of the tubes and cause heat exchange fluid leaks.
In contrast, Mannoni, et al, also describe the concept where the fill ratio is considered to be too low. That is, the fill ratio is less than 0.8. In this situation, the material that is welded is insufficient to fill the space between the butt surfaces of the bonding portions, thus giving rise to openings that can cause heat exchange fluid leaks by means of the collector plate.
As with Mannoni, et al, and other heat exchange assembly processes for plastic tube exchangers, full plates are utilized, with holes required for the insertion of the tubes through the holes. The holes are then sealed with either a heated wire, glue or the like. This is considered to be an extremely slow and labor intensive process. Accordingly, it would be advantageous if a design utilized for the end plate would be made of preformed inserts, allow for the tubes to be quickly assembled and then sealed with, for example, compression processes.
Various other types of systems employing heat exchanging concepts have been developed and are known in the industry. For example, Stark, U.S. Pat. No. 6,182,747 issued Feb. 6, 2001 discloses an air-to-air heat exchanging system utilizing a first airstream and a second airstream. The system includes at least two air-to-air thermal energy exchangers, with each having heat conducting walls, secured to a frame. The system can be characterized as having crossflow thermal energy exchangers with a series of parallel channels alternately blocked and enclosed within a housing. In this manner, one airstream is forced to be directed through the exhaust air channels, and a second airstream is directed through the supply air channels. This occurs in a substantially crossflow arrangement, and can further be characterized as a plate-type thermal energy exchanger system. In addition to the foregoing, the Stark system includes arrangement of a number of the thermal energy exchanger units in a side-by-side configuration, with a manifold for purposes of dispersing and gathering the related airstreams to a plenum chamber, so as to reduce the size of the system and the energy requirements for operating the system for conditioning a large volume of air.
Stark further describes what he considers to be prior art to his own thermal energy exchanger system. For example, Stark describes the concept that a number of different devices that exchange heat between airstreams are relatively well known, whereby stale air is exhausted from a building source as an energy source for heating or cooling incoming outside air.
Stark further describes the concept that there currently exists a number of crossflow plate-type air-to-air thermal energy exchangers. These known devices can be constructed of plastic or metal for heat exchange or alternatively, can be constructed of a homogenous material (such as paper) for a latent energy exchange. In the prior art thermal energy exchangers, Stark describes the concept that a large space is generally required, for purposes of housing the large plate crossflow thermal energy exchangers. As plates of a plate thermal energy exchanger increase in size, and for a given efficiency, the space in between the plates must increase in distance. Correspondingly, such increase in plate spacing results in a significant increase in the entirety of the volume of the heat exchanging apparatus.
Stark further explains that volumetric efficiency quantifies as the required equipment volume in a “per unit of capacity” at a given performance level. In plate-type crossflow air-to-air thermal energy exchangers, and for purposes of increase in the volume efficiency and economy of the unit, the smallest possible plate size should preferably be used. However, crossflow thermal energy exchangers with smaller plates generally require additional length (i.e., additional plates) for handling air volumes equal to those of units having larger plates. However, increase in the plate size will require a relatively larger installation space, which may then limit the performance of the thermal energy exchanger. Also, when using crossflow plate-type air-to-air thermal energy exchangers with smaller plates, the length, or number of plates, typically exceeds the allowable dimensions or number of plates.
In the Stark system, certain of the disadvantages associated with systems known prior to Stark are allegedly obviated. More specifically, Stark describes the concept of providing a plate-type crossbow air-to-air thermal energy exchanger with a series of plates, while maintaining a seal between the intake channel and exhaust channels. Stark also describes the concept that the thermal energy exchanger facilitates installation in a system which utilizes a relatively small number of units, so as to reduce the size required for installation, while correspondingly providing a relatively efficient operating and economical system for recovering heat in buildings, such as homes and offices.
In summary, the apparatus described in Stark can be utilized as a thermal energy exchanger, where intake air is heated or cooled in a plate thermal energy exchanger, using the heat energy in the exhaust air. The exhaust air flow travels through the exhaust channel, of which at least one wall of the channel represents the wall separating the intake channel from the exhaust channel. It is through this wall that the heat exchange process occurs.
A series of conducting walls are arranged face to face, and then also arranged in a side-by-side configuration, in rows so as to complete the necessary amount of heat exchange space. The number of intake and exhaust channels is determined by the amount of plates provided, which is variable with respect to the installation. Stark describes the concept that a square shape for the thermal energy exchanger is preferably positioned on a point of the square, so that a diagonal running from one corner of the square to its opposite corner is generally vertical when the unit is installed.
The thermal energy exchanger plates are disclosed as being spaced apart by a series of corrugations extending between the walls and in thermal contact with each of the walls. The corrugations serve the dual purpose of enhancing heat transfer between the walls, and also providing flow paths for the airstream to seal the intake channels from the exhaust channels. Stark describes the concept of the preferred arrangement as a crossflow, where the air path and intake channels are arranged at right angles to the air path and exhaust channels. In this manner, the flow path through the heat conducting walls is defined so that the intake air flow is substantially in a crossflow arrangement from the exhaust air flow. Stark also discloses the concept that the Stark configuration may use two manifolds, consisting of entrance and exit ports for the intake airstream and entrance and exit ports for the exhaust airstream. The flow pattern through the apparatus is considered to be a function of how the manifolds are baffled in relation to one another. The flow pattern may be arranged for either crossflow or parallel flow.
Thunberg, U.S. Pat. No. 4,391,321 issued Jul. 5, 1983 discloses another thermal energy exchanger for use in ventilating interior structures. The thermal energy exchanger is utilized in combination with a two duct system, for bringing relatively cold outside air into an enclosure, while exhausting relatively warm room air from the enclosure. The thermal energy exchanger is positioned so as to recover heat from the exhaust air into the incoming cold fresh air. Specifically, Thunberg discloses the concept of employing a valving system which switches the incoming cold air with the warm exhaust air in the flow paths of the thermal energy exchanger. Thunberg describes the concept that this valving configuration allegedly solves the problem of moisture from the exhaust air condensing on the walls of the ducting system for the exhaust air.
Martin, et. al., U.S. Pat. No. 4,336,748 issued Jun. 29, 1982 discloses an exchanger for exchanging a first fluid with a second fluid, in varying proportions. A first duct carries the first fluid, while a second duct carries the second fluid. A transfer chamber is connected to both ducts through which some or all of the second fluid is able to be transferred back into the first duct. A variable control system is provided in the form of first and second damper blades in the chamber which can be swung together, thus dividing the chamber and preventing transfer. The blades can correspondingly be swung apart so as to provide for varying proportions of the transfer. The chamber also has an inlet means for inlet of the first fluid, and outlet means for discharges of the second fluid.
Goldsmith, U.S. Pat. No. 3,934,798 discloses a heat exchanging system for use with a forced draft home heating system. Air is directed from a return register to the return plenum through a thermal energy exchanger interposed in the line of the flue. The thermal energy exchanger includes an enlarged casing extending between tapered collars, and enclosing heat exchange tubes having approximately the same cross sectional area as the flue.
George, U.S. Pat. No. 4,334,577 issued Jun. 15, 1982 discloses a ventilation system for a livestock house. The system includes a thermal energy exchanger whereby, prior to entering the thermal energy exchanger, warm moist air from the interior passes through a filter device that removes particulates. In this manner, the particulates do not combine with condensation in the thermal energy exchanger, so as to block the thermal energy exchanger. Fresh air, received from the outside, and after being warmed in the thermal energy exchanger, passes into an elongated distribution plenum located slightly below the ceiling of the livestock house. This plenum contains apertures which direct the fresh air horizontally into the housing area. The upper surface of the plenum is located directly below an elongated opening in the ceiling. Along each side of the opening, baffles are hinged to the ceiling. The baffles extend obliquely outwardly and downwardly, and contact the upper surface of the plenum at their lowermost edges. With this configuration, warm moist air from the building is prevented from escaping through the opening and into an attic area above the ceiling. However, when exhaust fans are energized to exhaust air from the living area, the withdrawn air is replaced by air from the attic. This air is passed into the living area by lifting the baffles and flowing outwardly over the horizontal upper surface of the plenum.
With an appropriate accommodation of tube designs and core plate designs, assembly speed can not only be facilitated, but other problems can also be overcome. For example, it would be advantageous to have the capability of eliminating the need for defrosting units in cold weather. If this problem could be eliminated, it would greatly reduce the overall cost of plastic tube exchanges, compared to other types of thermal energy exchangers on the market. Elimination of the defrost cycle and related parts would allow for the use of all plastic housing and axial fan components. Accordingly, an “all plastic” thermal energy exchanger or “heat recovery ventilator” (“HRV”) could be made available. Such a thermal energy exchanger would have numerous advantages. For example, one of the by-products of air-to-air heat exchange is condensation on the inside of housing and tubes. With metal housings, units are subjected to rust, eventually resulting in the mixing of the airstreams and ultimate failure of the HRV unit. With an all plastic assembly, the longevity of the HRV or thermal energy exchanger is increased, due to the elimination of components subject to rust.
Another aspect of air-to-air thermal energy exchanger assemblies is that the longer the air can stay within the core, the “more efficient” the actual exchange will function. In this regard, it would be advantageous to have some type of assembly or design which would improve exchange rates between the two airstreams. Another aspect of providing for more efficient exchange of thermal energy relates to surface areas of surfaces which separate fresh airstreams from stale airstreams. That is, the greater the surface area of the material which separates the stale airstream from the fresh airstream, the higher will be the flow rate of thermal energy between the airstreams.
In addition, it would also be advantageous to undertake tube designs which will improve relative cleanliness. Known plate core designs accumulate dirt and dust particles, which eventually plug up the core and reduce exchange efficiency and air flow. Such known thermal energy exchangers are then relatively difficult to clean, because such cleaning requires the disassembly of the unit periodically so as to maintain efficiency. In this regard, it would be advantageous to utilize a tube design which reduces the frequency of necessary cleaning, and also facilitates cleaning when required.
In accordance with all the foregoing, it would be advantageous to utilize a core end plate and tube design which facilitates assembly, runs efficiently, and is of a relatively low cost. In this regard, it would be advantageous for such a thermal energy exchanger to have relatively few moving parts, and not be susceptible to wear, such as rust processes.
In accordance with the foregoing, it is advantageous to provide for a thermal energy exchanger meeting these advantages. In this regard, and with reference to the core, a thin wall plastic tube may utilize “film heat transfer” technology, so as to pass heat from one airstream to another, without mixing the air at a rate comparable to that of aluminum. Such a tube design has advantages over other plastic cores on the market, because it provides for a greater surface area than current plate technology. Also, due to the internal diameter of the tube, it will reject “freeze-up” in cold weather, which require defrosting cycles.
More specifically, with the use of plastic tubes having relatively thin walls, the internal diameter of each tube is relatively larger than would exist with tubes having relatively thicker walls. Still further, if the tubes can be supported and constructed so as to provide for additional and larger spaces between and around the tubes, freeze-up can again be significantly reduced. This feature can result in financial savings not only in that fewer or no defrosting cycles are required, but also that the use of a fan may not be required whatsoever.
With respect to the end plates, it is advantageous to utilize a design where the end plate is made up of preformed inserts, allowing for the tubes to be quickly assembled and sealed with compression. Such a design will work with current plastic tubes, and with enthalpic tubes known to be utilized for energy recovery ventilators, as well as metal tubes such as copper or aluminum without design changes to the overall unit.